Engine fuel control for internal expansion engine fuel systems



D. N. WALKER 3 Sheets-Sheet J,-

ENGINE FUEL CONTROL FOR INTERNAL XPANSION ENGINE FUEL SYSTEMS .www

June 23, 1953 Fnd oct. 3o, 1945 D. N. WALKER June 23, 1953 ENGINE FUELCONTROL FQR INTERNAL EXPANSION ENGINE FUEL SYSTEMS Filed' oct. so, 1945fs sheets-sheet 2 jijlw. M M W M Il. 'il

June 23, 1953 n. N. WALKER 2,642,719

ENGINE FUEL CONTROLl FOR INTERNAL EXPANSION ENGINE FUEL SYSTEMS FiledOct. 30, 1945 5 Sheets-Sheet 3 F26. 4, 2 4/-' 406\ o 4/6 439' 45g I'4/,4 450 .l O) (D F 40 44 45A (C) i l' 10" '406 54a A 4 55 I .5f- O r IMJLW Patented June 23, 1953 ENGINE FUEL CONTROL FOR INTERNAL EXFANsIoNENGINE FUEL SYSTEMS Daniel Norman Walker, Ashby Parva, near Rugby,rk

England, assignor to Power Jets (Research & Development) Limited,London, England Application October 30, 1945,4Serial No. 625,5'50

` In Great Britain August 14, 1942 Section 1, Public Law 690, August 8,1946 Patent expires August 14, 1962 6 Claims.

This invention relates to pressure-sensitive control devices for aeroengines and more particularly to devices which are required to operatein accordance with the ambient pressure of air, for example inaccordance with atmospheric pressure at varying altitude, atfthe sametime being dual controlled by an operator or possibly by governingmeans.

In certain throttle or fuel supply systems of aero-engines, and insimilar cases, it is sometimes required to provide means Iby which acontrol device can be operated (and may require a substantial effort tobe operated) in accordance with the ambient pressure and also by hand.

Previously such control has been accomplished in some cases by the useof a barostatic capsule controlling a valve system which in turncontrols a servo-fluid, the pressure of which affords operative effort,the dual control being a separate system. Such devices have theirdraw-backs and it is an object of this invention to provide controlmeans of a simple and reliable nature which in many applications willnot require any servomechanism or which may be said to be itself aservo-mechanism and which is Well adapted to the provision of dualcontrol such, for example, as further manual control.

The invention is ameans for controlling an aero-engine, more especiallythough not exclusively one in which fuel is supplied under considerablepressure, of which the fuel consumption n varies greatly in accordancewith altitude, and of which the running speed (R. P. M.) is determinedby the rate of fuel supply, it is proposed in one such case, to employthe invention as a means for controllingthe relief valve whichdetermines the fuel pressure and therefore rate of supply to the engine.Alternatively, a variabledelivery fuel pump may be the thing controlled.In cases in which suitable characteristics exist, the system may beemployed as a speed-governing system which reacts to ambient pressure.It should, however, be pointed out that the invention may be foundtohave other applications such, for example, as :the dual control of boostpressure of aero-engines, or lother aero-engine control devices, theoperationof which has to be related to altitude or ambientpressure.

The underlying'idea of the invention is the use of an independent airpump which for any given conditions of running is a pump of constantcompression ratio (so that its output pressure is a function of ambientpressure) to operate a required device, such as a variable spring loadon a relief valve or directly'c'ause the load on -.tion and response asthe R. P. M. increases.

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the valve whilst means are further Provided for affecting dual controlof such device, for example manually. The second or dual control mayaffect the delivery of thepump itself as creating variations ofeffective compression ratio, or may affect the device controlled in partbythe pump output by direct operation.

'I'he term independent in connection with the air compressor means thatthe compressor does not take part in the supply of air as Working fluidin the engine, that is to say, the independent compressor is differentfrom any compressor which is in the nature of a supercharger orprecompressor of working fluid.

The invention has an important application to an aero-engine of the kindcomprising a compressor, combustion arrangement, and gas turbine, allarranged as a jet-propulsion power plant. Engines of this kind have afuel supply system at comparatively high pressure, in which the rate offuel delivery is determined bythis pressure, and is, moreover, requiredto be reduced substantially with every increase of altitude. In such anengine there is an engine-driven positive displacement fuel pump (e. g.a gear pump) with sufficient capacity to deliver the maximum enginerequirement with a marginfor safety. It is to be notedfthat suchenginesr may have relatively limited rates of acceleration when theyarel running inthe lower range of their speeds. That is to say, they mayhave a poor throttle response at lowR. P.`M. and improving accelera- Itfollows that ideally the control system should prevent excessiverates ofincrease of rate of fuel delivery in the lower speed ranges, and this isa matter which the invention can look after. In'

applying the invention there' is provided as independent compressor asingle-cylinder air pump driven positively at constant speed ratio bythe engine. This pump has its intake opened to the ambient atmosphere,i. e. that whichthe engine is supplied with air, delivers to avolumetric capacity and thence to a cylinder in which works apistonwhich controls the load on a relief valve in the fuel supply line.Manual means are provided for varying the air pump compression ratio.The operation ofthe device is as follows:

Assume the engine to be running and the relief valve spring setting tobe such that in the idling condition, and lwith the minimum air pumpcompression ratio, the fuel pressure is appropriate to idling. When itis desired to accelerate the engine the air pump compression ratio isincreased and its delivery pressure therefore increases.

whereupon the relief valve spring load is increased and the fuelpressure rises, in turn causing the engine to accelerate until a higherstable speed is reached. The effect ofthe capacity mentioned is toprevent unduly rapid increase of rate of fuel supply at low engine (andtherefore pump) R. P. M. In higher ranges of R. P. M. however the airpump speed being higher the capacity is proportionally less effective asa delaying factor to pressure rise.

Now let it be supposed that with stable engine speed and without furtheroperation of the manual control, the altitude is increased and thereforethe atmospheric pressure is decreased. Theair pump, now operating withconstant compression ratio, will deliver less pressure so that therelief valve spring load will decrease and the fuel supply pressure willcorrespondingly decrease. Conversely, if altitude is now decreased, thefuel pressure wil automatically increase. At all times the manualcontrol can be used to adjust the fuel pressure and it therefore assumesthe function of a throttle control.

It will be evident from the foregoing brief description that the airpump device Vmay have other applications or other uses in the givenapplication; for example, a tapping from the delivery of the pump may beused to operate lother devices which vare required to respond inproportion to atmospheric pressure such as aircraft cabin pressure orpressure above the fuel in fuel tanks, instruments, or the like.

The drawings illustrate theinvention as it may be applied in oneembodiment, together vwith schematic diagrams to illustrate the functionof the device and to indicate an alternative application.

Fig. 1 is a diagram illustrating a fuel system embodying the invention.

Fig. 2 diagrammatically illustrates an independent compressor and reliefvalve to demonstrate the function,` according to one application, of theinvention.

Fig. 3 diagrammatically illustrates an independent compressor and reliefvalve to demonstrate an alternative function and mode of use.

Fig. 4 is a sectional view of an actual compressor intended for useinaccordance with the function of Fig. 2. I

Fig. 5 is a sectional view of a relief valve adapted for use with thecompressor of Fig. 4.

Referring first to Fig. l, the vfuel system as a whole comprises asupply tank I, from which the fuel is delivered through a motorisedcentrifugal low-pressure pump 2v through a low-pressure filter 3 to themain fuel pump 4 which is an engine driven positive displacement pumpsuch as a gear pump. The fuel pumped at 4- is taken by the mainhigh-pressure pipe 5to the body of a relief-valve 6, which controls thepressure in the pipe 5. Fuel passing through valve 6-is returned to thetank by return or spill-pipe 1. Fuel at the required delivery pressureVflows through a high pressure filter 8, a centrifugal or other governor9 (if required) and a shut-off cock IU to a burner manifoldinterconnecting burners |I. Such. a fuel system, correspondsvsubstantially with known practice, but no throttle valve is provided,this function being replaced by the invention, in that the load onrelief valve 6, is

variable and is attributable to the output pressure of an independentair compressor |2which has a variable compression ratio adjustable by acontrol lever (IZA) and is itselfv driven by the engine tn which fuel issupplied. .The engine may '4 be a gas turbine aero engine wherein theoutput from an air compressor |4 is brought to combustion together withfuel injected by burners in combustion chambers I 5, the hot gases thendriving a turbine |6 which itself drives the compressor I4, and beingfinally ejected to atmos- 'phere at an outlet |1 to form a propulsivejet stream. For a special purpose later stated, an air capacity chamberI3 may be interposed between the compressor I2 and valve 6.

In Fig. 2, is represented a compressor and relief valve for use at I2and 6 in Fig. l, drawn to demonstrate function, and shows a possible,though not a preferred, Way of connecting the compressor to the reliefvalve. The compressor is a single acting reciprocating compressor withcylinder 20, piston 2|, and connecting rod 22, driven by a crank 23. Thepiston 2| is upwardly skirted and this skirt has an outlet port ring 2|Ato register with an annular outlet port 20A in the cylinder 20, which isconnected to a ram cylinder 24. The cylinder 20 has an inlet port 20Bfrom atmosphere. In the cylinder 24 is a spring loaded ram 25 whichoperates a sliding cam 25A, arranged to bear on a follower 26, themovement of which are transmitted to a compression spring 21 to vary theload therein, which load is applied to a relief valve 28 in a branchduct oif the main fuel line 5. Slidable in the top of the cylinder 20 isa movable compression head 29 which has an extension within the skirt ofthe piston 2| to maintain a reasonably high order of compression ratio,the head 29 is urged outwards by a spring 29A against an operators cam25B, rotation of which enables the user to vary the compression ratio ofthe compressor. The crankshaft 23 being positively driven by the engineto which the fuel is being supplied, the speed of which is a function ofthe rate of fuel supply, the following describes the function of thisdevice.

At starting, the fuel pump 4 raises the pressure in pipe 5, up to thatwhich is maintained by the spring 21 on the relief valves 28. This isestablished to be a suitable starting and/or idling p-ressure. As soonas the engine is properly running, the compressor being now driven,tends to urge the ram 25 outwards, the effective extent to whichv itdoes so being controlled by the spring of this ram, the shape of the cam25A and the spring 21, and the pressure of air delivered by thecompressor. In the starting or idling condition the head 29 is fullyout, the compressor pressure-rise from atmospheric being too slight tohave an effect on the relief valve 28. Now if the operator by rotatingcam 29B closes down the head 29 the compression ratio of the compressor,and therefore the delivered pressure. increases. The effect of this is,at some stage, to move the cam 25A (to the right) thereby loading up therelief valve 28 by compressing the spring 21. Consequently the fuelpressure in pipe 5 rises, and more fuel is passed to the burners I l sothat the engine responds by accelerating until a new stable speed itreached.

It is clear that the cam 29B has the functional nature of a throttlecontrol in that it controls the engine speed. If the head 29 is allowedto move outwards, the compression ratio being reduced the compressorwill actually pass air backwards from the ram cylinder 24 to atmosphere,until stability occurs at a reduced engine speed.

It seems hardly necessary to describe the rela-- tionship of the piston2| and the ports 20B, 2 IA which represent a standard arrangement for asimple compressor.

Now let it be supposed that the device 'is operating and the enginerunning at a selected speed in a climbing aircraft. The atmosphericpressure is progressively decreasing as altitude increases. It followsthat the delivery pressure from the compressor decreases likewise (thecompression ratio being, for the time being, fixed) so that the load onvalve 28 is progressively reduced, and the pressure in pipe 5correspondingly reduced.- Thusr the rate of fuel supply is automaticallyvaried with change of atmospheric pressure at the compressor intake.This corresponds with the fuel requirement of the engine, so that theengine speed may remain constant despite the change of altitude.

The foregoing, as well as describing the operation of the particularform of the device, well exemplifies the main object of the invention,in that it demonstrates the dual function of operators speed control andautomatic altitude response. B'y particular selection of compressorcharacteristics, cams, spring ratio, and burner pressure/nowcharacteristics the employment of a speed governor such as 3, may beobviated, but it is at present regarded as desirable to provide it as a'top speed governor in the interests 'of engine safety.

Turning now to Fig. 3, wherein as many of the same references are usedas possible, an al-k ternatively functioning scheme is depicted. Hereagain are a compressor and a relief valve, but the compressor is of.fixed compression ratio. In this case its ram operates the cam 25A overa follower 30 on one end of a lever 3I the fulcrum of which at SIAreacts on the relief valve spring.

The other end of the lever 3| has asecond cam follower 32 cooperatingwith an operators cam 33. The relief valve load is thus applieddifferentially by the eifect ofthe compressor delivery pressure (whichas shown varies with altitude) and the effect of the cam 33, which isunder the operators control. The arrangement presupposes that the forcesapplied by either cam cannot be such as to result in resultant movementof the other. Then if cam 33 be moved to depress the follower 32, moreload is applied in spring 21 with consequent increase of engine speed byvirtue of increased fuel pressure.

Also, however, changes of altitude affect the position of the cam 25Aand these in turn affect the load on the relief valve. Thus again isseen the operator controlled function and the altitude controlledfunction.

In yactual practice, it is proposed not to employ the cam mechanism ofFig. 2. As will be gathered from Fig. 1, (later to be arnpliiiedfby`reference to Figs. 4 and 5) the'prcposed practice is to lead thedelivery from the compressor more directly to load the relief valvespring. If in such an arrangement, and air capacity chamber(I3 of Fig.l) is interposed in the air connection berateI atfwhich the' compressorpressure builds up onthe relief valve, and a factor Within this is thedriving speed of the compressor.v Thus at low engine R. P. M. therelief-valve-controlled pressure rise (via pipe 5) is limited,preventing the operator from'too rapidly increasing the fuel supply,whilst at higher R. P. M. thetime-lag (due to the capacity I3) isproportionately less, so that virtually immediate response to operatorsmovement is approached. In the converse case of deceleration of R. P.M., the capacity I3 -may serve a, further useful` purpose in preventnwhich has inlet ports 4IAconnected to an inlet passage 40A of the body40, a protectedcavity 40 serving to prevent ingress of foreign matter.

The `cylinder hasy outlet ports IIB connecting through an annular spaceto ar suitable outlet union provided through the body 40, and notillustrated except diagrammatically as a passage 40C. The top end of thecylinder 4I is open to a passage 42A which connects to a valve cylinder42the upper end of which is open to atmosphere through perforations in aprotective cap 42B.

The piston 43 of the compressor is worked by a connecting ,rodk 43Adriven by a crank 43B through crankpin 43C. The crank is engineu driven.The piston 43 is ported at 43D through its upwardly extending skirt 43E,the ports registering alternately with the ports 4I A and 4IB at bottomand top of stroke.r Articulated on the crankpin 43C lsa link lever 44,to which is pivoted a valve rod 45A to reciprocate the valve 45, whichslides in the valve cylinder 42. vThe outer end of the'link lever 44 islocated by a link 44A adjusted by a crank 44B on an operators spindle44C-borne in the body 40. Rotation of the spindle 44C alters the settingof the valve 45,k

the functionof which is to cut off the passage' Y 42A during a greateror lesser part of the strokek of piston 43. If, for example, it werearranged that the valve 45 could be left so low that the passage 42A isnever cut off, no compression results. By progressively raising thevalve 45 the effective compression ratio of the compressor is under fullcontrol. A compression head 46 is provided, to reduce the effectiveclearance volu ume of the compressor so as toV give a higher y maximumcompression 'ratio `whilst preserving tween compressor and relief valve,another function can be introduced, namely control of acceleration. Itis to be understod that in some cases of engines with this type of fuelsystems, the ability to accelerate rapidly from low R. P. M. is somewhatdefective, at least if excessive temperatures are not tolerable. On theother hand, in a higher range of R. P. M. acceleration can be very rapidwithout excessive temperatures. A capacity such as I3 can be made toprevent excessive rate of increase of rate of fuel supply in the lowerspeed range, because if the capacity of the compressor I2 is small inrelation to that of I3, a marked time factor is introduced in thepracticable dimensions and a reasonably long Ibody 50 is 'a Tconnection, two lateral branches of which pass the main fuel supply(indicated by arrow) whilst the third, upward, branch forms a guidepassage and seat for the relief valve 5I. Within the body 50 above thevalve 5I, is a. space from which fuel which has passed the valve escapesby the passage indicated at 52 tov i return` to the fuel tank (by pipe'I of Fig. 1.) Above this space is a guideway for a pushrod 53 which ismade as nearly as possible a i'luidtight through slidable t in theguideway. 'I'he pushu rod 53 bears on the centre of the valve 5ldownwards mid reacts upwards against a hard steel plate 54A inserted ina .central pocket of a diaphragm plate 54 which partially supports anannular flexible diaphragm 54B, the periphery of which is secured :inthe body 58. Below the diaphragm constituted by 54-54B is an air spacebreathed and drained by a passage 55 to atmosphere or through a pipe toany'desred place. Above the diaphragm is a pressure space 56 whichhouses a spring l which exerts a selected load downwards on thediaphragm plate 54 and through `rod 53 on to the valve 5|. This springload determines the minimum pressure at which the valve 5I will open,and the rate of the spring may also somewhat modify the precisebehaviour of the .system in various running conditions. The connectionat 50A leads to the pressure space 56, thus submitting the diaphragm asa whole to a downward pressure which is transmitted to the valve 5I as aload additional to that of the spring `51. This relief valve is thusvariable as to its blow-off pressure, in accordance with the pressuregenerated by the compressor. .In function the arrangement `will be seento lbe practically the same as the arrangement of Fig. 2.

The mechanical aspects of .the device have not been described in greatdetail, there being nothing involved which calls for the application ofmore than ordinary engineering skill and technique. It will be obviousthat lubrication, protection against dirt, etc., will be provided asrequired, and that provision may be made for adequate access foradjustment replacement or inspection of working parts.

I claim:

1. A fuel flow control system for airplanes comprising an engine, a fuelpump, a fuel supply line connecting said fuel pipe and engine, a fuelregulator in said line, an expansible chamber positive displacement aircompressor having a chamber, said compressor being driven from saidengine at a speed in xed proportion to the speed of the engine, meansdefining a closed pressure zone, the chamber of said compressor beingalternately in free communication with atmosphere and said closedpressure zone, and means movable in response to pressure changes in saidzone for actuating said regulator,

2. An engine fuel control for an internal expansion engine fuel systemincluding a fuel supply, conduits for said fuel, and anengine drivenfuel pump supplying said engine with fuel at a pressurecomprising apositive displa-cement type air compressor driven by said engine andaspirating from ambient atmosphere and with its delivery pressure`arranged as a predetermined function of the inlet air pressureirrespective of engine speed and of inlet pressure and functioning as anair compressor solely for said engine fuel control, a compressed airreceiving means defining a vessel closed to ambient atmosphere but indirect communication with said compressor for receiving said compresseddelivery air, an engine fuel flow control device connected in said fuelsystem conduit having means to control the fuel flow therein and havingfuel flow control actuating means arranged in association with saidcompressed air receiving means to aetuate said fuel flow control meansin response to the compressor delivery pressure in said receiving means,compression ratio varying means in said compressor to vary the deliverypressure and manual means for actuating said compression ratio varyingmeans for varying said compression ratio and in consequence for varyingsaid delivery pressure and said fuel flow, the arrangement being suchthat the engine fuel flow is controlled in accordance with the magnitudeof any pressure change caused by a change in both intake pressure and incompression ratio of said compressor.

3. An engine fuel control according to claim 2 wherein the saidcompressor is of the cylinder andreciprocating piston type and the saidcompression varying means comprises mechanism associated with saidpiston and cylinder for varying the clearance volume of said compressor.

4. An engine fuel control according to claim 2, wherein the compressoris of the cylinder and reciprocating piston type and said compressionvarying means comprises a movable compression head slidable in saidcylinder to vary the clearance volume of said cylinder and spring urgedin a direction to increase the clearance and decrease the compressionratio and manually urged in opposition to said spring to decrease theclearance and increase the compression ratio.

5. An engine fuel control according to claim 2, wherein said engine fuelflow control device comprises a fuel pressure relief valve in saidconduit and an air pressure loading means influenced by said compressordelivery pressure in said receiving mea-ns to load said pressure reliefvalve.

6. An engine fuel control according to claim 2 wherein the said fuelflow control device comprises a spring loaded fuel pressure relief valvein said conduit and a pressure loading piston in a cylinder influencedby said compressed delivery pressure in said receiver to load saidspring.

DANIEL NORMAN WALKER.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,510,688 LaFon Oct. 7, 1924 1,920,752 Kissing Aug. l, 19332,219,994 Jung Oct. 29, 1940 2,397,835 Brame Apr. 2, 1946 2,400,413Hersey May 14, 1946 2,400,416 Hersey May 14, 1946

